Method for producing ethylene vinyl acetate copolymer

Abstract

To provide a method of preparing an ethylene vinyl acetate copolymer, as a solvent, using alkyl acetate, which has a low chain transfer constant and is easily separated from monomers in an ethylene vinyl acetate polymerization process and to provide a method of preparing an ethylene vinyl acetate copolymer that easily controls the molecular weight of the ethylene vinyl acetate copolymer and is applicable to ultra-high molecular weight ethylene vinyl acetate copolymer rubber.SOLUTION: There is provided a method of preparing ethylene vinyl acetate copolymer, comprising the step of adding a monomer comprising ethylene and vinyl acetate, and a solvent comprising alkyl acetate to a reactor and performing polymerization.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing an ethylene-vinyl acetate copolymer. [Background technology]

[0002] Ethylene-vinyl acetate copolymer (EVA) is a polymer copolymer in which ethylene and vinyl acetate are randomly copolymerized. It is known to exhibit properties similar to rubber due to its excellent flexibility and elasticity. Such EVA copolymers exhibit different physical properties depending on their molecular weight or vinyl acetate content. They generally have excellent transparency and adhesive strength, making them suitable for a variety of applications, including solar cell encapsulants, shoe soles, coated paper, and agricultural films. High-molecular-weight VACs can be used for specialized applications, such as submarine cables. EVA copolymers with a high VAC content can be converted to ethylene-vinyl alcohol (EVA), which has excellent gas barrier properties, by an additional saponification reaction. The resulting EVA copolymers, with their excellent gas barrier properties and chemical resistance, can be used in a wide range of applications, including films, containers, and fibers. They are particularly useful in applications requiring gas barrier properties, such as fresh food packaging and automobile gas tanks.

[0003] Generally, ethylene-vinyl acetate copolymers are industrially produced by high-temperature, high-pressure gas phase polymerization or low-temperature, low-pressure solution polymerization using vinyl acetate monomer, ethylene, and an initiator as raw materials. In particular, ethylene-vinyl acetate copolymers with a high vinyl acetate content are generally produced by low-temperature, low-pressure solution polymerization, in which a C1-C4 alcohol is used as an additional solvent.

[0004] The purpose of using an additional solvent in a solution polymerization process is to reduce the viscosity in the polymerization reactor and effectively remove the heat of polymerization generated during the ethylene vinyl acetate polymerization process, and it is generally used at 2 to 20 wt% of the total reaction medium. Depending on the type of alcohol used, a chain transfer reaction occurs in which the active sites of the polymerization reaction move to the alcohol. This chain transfer reaction leads to the termination or branching of polymer growth, hindering the increase in molecular weight of linear polymers.

[0005] To prevent this phenomenon, a method of using an alcohol with a low chain transfer coefficient, such as tert-butyl alcohol, alone or in combination has been proposed. However, due to its relatively high cost, high boiling point, and the formation of an azeotrope with the monomer, separation efficiency in subsequent processes, especially in the unreacted monomer recovery process, is reduced, making it difficult to apply. Summary of the Invention [Problem to be solved by the invention]

[0006] Therefore, the present invention aims to provide a method for producing an ethylene-vinyl acetate copolymer using, as a solvent, an alkyl acetate which has a low chain transfer constant and is easily separated from the monomer in the ethylene-vinyl acetate polymerization step.

[0007] Furthermore, the present invention provides a production method that makes it easy to adjust the molecular weight of ethylene-vinyl acetate copolymers and is applicable to rubbers of ethylene-vinyl acetate copolymers having ultra-high molecular weights. [Means for solving the problem]

[0008] One embodiment provides a method for producing an ethylene vinyl acetate copolymer, including the step of introducing monomers including ethylene and vinyl acetate, and a solvent including an alkyl acetate into a reactor and polymerizing the monomers.

[0009] The alkyl acetate may have a boiling point of 57°C to 126°C.

[0010] The alkyl acetate may be at least one selected from ethyl acetate, methyl acetate, propyl acetate, butyl acetate, and dimethyl acetate.

[0011] The solvent may be added in an amount of 2.5% by weight to 50% by weight based on the total amount of the monomer and the solvent.

[0012] The polymerizing step may further include adding an initiator including an azobis-based compound, benzoyl peroxide (BPO), or a combination thereof, and the azobis-based compound may include azobisisobutyronitrile (AIBN), azobisdimethylvaleronitrile (ADVN), or a combination thereof.

[0013] The weight average molecular weight (Mw) of the ethylene vinyl acetate copolymer may be 150,000 g / mol to 500,000 g / mol.

[0014] The ethylene vinyl acetate copolymer may contain 40 mol % to 80 mol % vinyl acetate. [Effects of the Invention]

[0015] According to one embodiment, the physical properties of the product can be improved by obtaining an ethylene-vinyl acetate copolymer with a high molecular weight, and it can also be applied to rubbers made from ultra-high molecular weight ethylene-vinyl acetate copolymers. Furthermore, by using this method, the unreacted vinyl acetate and the alkyl acetate solvent do not form an azeotrope, making the subsequent separation process easier. DETAILED DESCRIPTION OF THE INVENTION

[0016] Although the present invention will be described in detail below so that those skilled in the art can easily implement the present invention, it should be understood that the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0017] According to one embodiment, the ethylene vinyl acetate copolymer may be prepared by introducing monomers and a solvent into a reactor and polymerizing the monomers, where the monomers include ethylene and vinyl acetate, and the solvent includes an alkyl acetate.

[0018] Conventionally, C1-C4 alcohols such as methanol have been used as solvents in the polymerization step to produce ethylene vinyl acetate copolymers. However, this method limits the control of the molecular weight of the ethylene vinyl acetate (EVA) copolymer, making it difficult to obtain a high molecular weight resin. Furthermore, unreacted vinyl acetate and the alcohol often form an azeotropic mixture, making it difficult to separate.

[0019] The term "azeotrope" is used in the usual sense in the art, i.e., a liquid with a specific component ratio, in which the component ratio of the solution and the vapor are the same when the component ratio remains unchanged at a constant temperature like a pure liquid. The equilibrium temperature, which is the boiling point of an azeotropic mixture, is called the azeotropic point. The azeotropic state, in which the component ratio of the solution and the vapor are the same, changes depending on the pressure, and the azeotropic point indicates the minimum or maximum value on the boiling point curve, which shows the relationship between the component ratio and the boiling point.

[0020] Meanwhile, according to one embodiment, a high molecular weight ethylene vinyl acetate (EVA) copolymer can be obtained by polymerization using an alkyl acetate with a low chain transfer constant as a solvent, thereby improving the physical properties of the product. Furthermore, since unreacted vinyl acetate and alkyl acetate do not form an azeotrope, separation is easy.

[0021] The alkyl acetate used as the solvent may have a boiling point of 57° C. to 126° C., for example, 57° C. to 102° C., or 57° C. to 80° C. By using an alkyl acetate having a boiling point within the above range as the solvent, an ethylene vinyl acetate (EVA) copolymer with a high molecular weight can be obtained.

[0022] The alkyl acetate used as the solvent may be, for example, at least one selected from ethyl acetate, methyl acetate, propyl acetate, butyl acetate, and dimethyl acetate, and more specifically, ethyl acetate or methyl acetate.

[0023] The solvent may be added in an amount of 2.5% by weight to 50% by weight, for example, 5% by weight to 30% by weight, 9% by weight to 30% by weight, or 9% by weight to 15% by weight, based on the total amount of the monomer and the solvent. When the solvent is added within this content range, an ethylene vinyl acetate (EVA) copolymer with a high molecular weight can be obtained during polymerization.

[0024] The polymerization may be carried out by further adding an initiator.

[0025] The initiator may include an azobis compound, benzoyl peroxide (BPO), or a combination thereof, and the azobis compound may include azobisisobutyronitrile (AIBN), azobisdimethylvaleronitrile (ADVN), or a combination thereof.

[0026] The ethylene vinyl acetate copolymer obtained by the polymerization may have a weight average molecular weight (Mw) of 150,000 g / mol to 500,000 g / mol, for example, 150,000 g / mol to 400,000 g / mol, 250,000 g / mol to 400,000 g / mol, or 350,000 g / mol to 400,000 g / mol. Ethylene vinyl acetate copolymers having a weight average molecular weight (Mw) within this range have improved physical properties and can be used to produce ultra-high molecular weight ethylene vinyl acetate copolymer rubbers.

[0027] The ethylene-vinyl acetate copolymer obtained by the polymerization may contain 40 mol% to 80 mol% vinyl acetate, for example, 56 mol% to 72 mol% vinyl acetate. Ethylene-vinyl acetate copolymers containing vinyl acetate within this range have improved physical properties and can be used for ultra-high molecular weight ethylene-vinyl acetate copolymer rubbers.

[0028] Specific examples of the present invention will be presented below. However, the following examples are merely intended to specifically illustrate or explain the present invention, and the present invention should not be limited by these examples. Furthermore, the details not described herein can be fully inferred by those skilled in the art, and therefore, the description thereof will be omitted.

[0029] (Production of ethylene vinyl acetate copolymer) Example 1 21.5 wt% of ethylene, 69.3 wt% of vinyl acetate, and 9.2 wt% of ethyl acetate with a boiling point of 77°C as a solvent were charged into a reactor, and a polymerization reaction was carried out under conditions of 60°C and an ethylene pressure of 40 kg / cm2 to produce an ethylene vinyl acetate (EVA) copolymer containing 71.3 mol% of vinyl acetate.

[0030] Example 2 An ethylene vinyl acetate (EVA) copolymer was produced in the same manner as in Example 1, except that methyl acetate having a boiling point of 57° C. was used instead of ethyl acetate used as the solvent in Example 1.

[0031] Comparative Example 1 An ethylene vinyl acetate (EVA) copolymer was produced in the same manner as in Example 1, except that ethanol was used instead of ethyl acetate as the solvent.

[0032] Comparative Example 2 An ethylene vinyl acetate (EVA) copolymer was produced in the same manner as in Example 1, except that methanol was used instead of ethyl acetate as the solvent.

[0033] Evaluation 1: Molecular weight measurement of ethylene vinyl acetate (EVA) copolymer In order to confirm the molecular weight of the ethylene vinyl acetate (EVA) copolymers prepared in Examples 1 and 2 and Comparative Examples 1 and 2, the weight average molecular weight (Mw) was measured using gel permeation chromatography (GPC). The results are shown in Table 1 below.

[0034] [Table 1]

[0035] From Table 1 above, it can be seen that the molecular weights of the ethylene vinyl acetate (EVA) copolymers prepared in Examples 1 and 2 are higher than those of Comparative Examples 1 and 2. Therefore, according to one embodiment, the ethylene vinyl acetate copolymer has a high molecular weight that is applicable to rubber, and the physical properties of the product can be improved.

[0036] Evaluation 2: Whether or not an azeotrope is formed between vinyl acetate and the solvent The following Table 2 shows whether the solvents used in Examples 1 and 2 and Comparative Examples 1 and 2 do not form azeotropes with vinyl acetate and can be separated by simple distillation, or whether they form azeotropes and must be separated using an extractant or the like.

[0037] [Table 2]

[0038] This confirms that Examples 1 and 2 do not form azeotropes and can be separated by simple distillation, but all of the comparative examples form azeotropes and require a separate separation process.

[0039] Although the preferred embodiment of the present invention has been described above, the present invention is not limited thereto, and various modifications can be made within the scope of the claims, the detailed description of the invention, and the accompanying drawings, and it is to be understood that these modifications also fall within the scope of the present invention.

Claims

1. The method includes a step of introducing monomers consisting of ethylene and vinyl acetate and a solvent containing alkyl acetate into a reactor and polymerizing the monomers, The solvent is added in an amount of 9% by weight to 15% by weight based on the total amount of the monomer and the solvent, The ethylene-vinyl acetate copolymer has a weight average molecular weight (Mw) of 150,000 g / mol to 500,000 g / mol.

2. 2. The method for producing ethylene-vinyl acetate copolymer according to claim 1, wherein the alkyl acetate has a boiling point of 57°C to 126°C.

3. 2. The method for producing an ethylene-vinyl acetate copolymer according to claim 1, wherein the alkyl acetate is at least one selected from the group consisting of ethyl acetate, methyl acetate, propyl acetate, butyl acetate, and dimethyl acetate.

4. The polymerizing step further includes adding an initiator including an azobis compound, benzoyl peroxide (BPO), or a combination thereof; 2. The method for producing ethylene-vinyl acetate copolymer according to claim 1, wherein the azobis-based compound comprises azobisisobutyronitrile (AIBN), azobisdimethylvaleronitrile (ADVN), or a combination thereof.

5. 2. The method for producing an ethylene-vinyl acetate copolymer according to claim 1, wherein the ethylene-vinyl acetate copolymer contains 40 mol% to 80 mol% vinyl acetate.

Images